1. Field of the Invention
This invention relates to the field of packaging and concerns more particularly a liquid-tight cardboard tray produced from a suitable cardboard blank and the process by which the blank is assembled.
2. Description of Related Art
Some food products, such as the meat of poultry, steak or liver, are usually packed in packaging in the form of trays associated with a protective plastic film.
These trays are generally made from a polystyrene type material, and although relatively cheap to produce, they do have the drawback of not being biodegradable or recyclable.
To overcome these drawbacks, cardboard trays have been suggested comprising a bottom that is generally rectangular and comprises four sides. Sealing at the corners is ensured by bellows which are folded back against one of the lateral walls and held in position by gluing.
These bellows are produced in two generally triangular portions. To maintain the volume of the tray, one of these portions is glued on the back and the other on the front, depending on whether they are positioned inside or outside of the tray.
This double application of glue complicates automatic assembly of the trays, the complexity involved calling for the use of bulky assembly machines and limiting the speed at which the trays can be assembled.
A liquid-tight cardboard container is described in document U.S. Pat. No. 1,959,613. Its corners are provided with bellows in two portions, one of which comprises an opening or cut-out allowing the other portion of the bellows to come into direct contact with the receiving side. Thanks to this feature, the volume of the packaging can be maintained by applying glue to only one side of the cardboard blank.
In this container, the bellows are folded back against the outside to avoid the presence of internal folds and to keep the cut edges of the blank that are likely to absorb liquid outside the internal volume. Given the leak-proof end use of this container, for packaging liquids for example, it is indispensable for the bellows to be positioned on the outside.
However, in relation to the assembly process of the packaging, particularly the application of glue to only one face of the blank, this structure cannot prevent liquid from seeping between the two portions of the bellows. Liquid is also able to rise up by capillary action and pass quickly into the heart of the cardboard via the upper cut edge, thus causing the component material to break, the packaging to sag and its contents to drain away. The presence of external bellows also makes this type of packaging unattractive.
Document U.S. Pat. No. 4,304,352 describes a similar structure in which the drawbacks of the above-mentioned container, particularly liquid seepage between the two portions of the bellows and the rising of said liquid by capillary action, are overcome by providing for recto-verso gluing.
In this leak-proof container, intended for packaging liquid or semi-liquid products, the upper cut-out provided in one of the portions of the bellows allows the other portion of the bellows to be glued on to the reception side in order to improve the strength of the corners. It also facilitates the assembly of the corners, in conjunction with the presence of an edge to receive a sealed cover.
In view of the intended use of this container, and for the reasons explained above in connection with document U.S. Pat. No. 1,959,613, its corner bellows have to be folded back against the outside of the container, Such a structure is not very attractive and limits the possibilities of applying exterior markings.
In addition, the recto-verso gluing of bellows makes for a particularly complicated assembly installation. The leak-proof containers described in documents U.S. Pat. Nos. 1,995,613 and 4,304,352 have very specific end uses that are different from those that are the object of the present invention. They are in fact adapted to packaging liquid products and must be associated with an occultation system in the form of a cover to retain the packaged product.